첨단 (주사)전자현미경 분석을 통한 산화 하프늄 기반 강유전 박막의 원자 수준 나노 도메인 구조 규명 연구

학위논문(박사) -- 서울대학교대학원 : 공과대학 화학생물공학부, 2024. 2. 박정원.Atomic-Scale Investigation of Nano-Domain Structure in HfO2-Based Ferroelectric Thin Films by Advanced (S)TEM Analysis Kunwoo Park School of Chemical and Biological Engineering The Graduate School Seoul National University This thesis delves into the fundamental understanding of ferroelectric properties in nanocrystalline HfO2 thin films, which are gaining significant attention in both academic and semiconductor industry circles due to their novel ferroelectric characteristics at sub-10nm thicknesses. This research not only explores the inherent properties of HfO2 films used in CMOS technology but also unravels the complex mechanisms underpinning the ferroelectric phase in these materials. Key findings include the stabilization of the ferroelectric phase through silicon doping, which leverages silicon's tendency to form strong covalent bonds with oxygen, thereby altering the phase stability in favor of the ferroelectric orthorhombic phase. Scanning Transmission Electron Microscopy (STEM) and Density Functional Theory (DFT) calculations confirm that silicon doping introduces monoclinic structural components into the orthorhombic phase, facilitating ferroelectric transition. Additionally, the study investigates the effects of oxygen deficiency on the ferroelectric switching properties of Si-doped HfO2 films. Controlled annealing experiments demonstrate that high-temperature processes enhance oxygen vacancies, thereby reducing the energy barrier for polarization flipping, as evidenced by STEM, Electron Energy-Loss Spectroscopy (EELS), and first-principles calculations. Furthermore, the research reveals that -oriented grains in yttrium-doped HfO2 (Y:HfO2) films induce a high-symmetry mixed-(R3m, Pnm21) phase, which enhances polarization under in-plane compressive strain. This phenomenon, along with the cooperative effect of nanoscale orthorhombic grains and high-symmetry phase grain boundaries, is crucial in determining the overall ferroelectricity of the Y:HfO2 film. In-depth analysis of ferroelectric domain networks and oxygen position mapping elucidates that polarization is suppressed at vertical domain walls, whereas horizontal domain alignment with zero-width walls shows active polarization. This thesis provides significant insights into the complex nature of ferroelectric HfO2 thin films, offering valuable implications for the future design and application of these materials in advanced semiconductor technologies. Keywords: Ferroelectric HfO2 thin films, nanocrystalline structure analysis, doping effects, high-temperature annealing effects, electron microscopy and spectroscopy, ferroelectric domain network Student Number: 2018-23882본 논문은 나노 두께의 HfO2 박막이 갖는 강유전 특성에 대한 심층적인 이해를 제공한다. 특히 10nm 이하의 두께에서 나타나는 이 박막의 독특한 강 유전 특성은 학계와 반도체 산업에 큰 관심을 불러일으키고 있다. 본 연구는 CMOS 기술에서 활용되는 HfO2 필름의 기본적인 특성 뿐만 아니라, 이 재료들의 강유전 상태를 형성하는 복잡한 메커니즘을 규명한다. 이 논문의 핵심 발견 중 하나는 실리콘 도핑을 통해 강유전 상을 안정화시키는 기작을 밝혔다는 것이다. 실리콘은 산소와 강한 공유 결합을 형성하는 경 향이 있으며, 이는 강유전 상의 안정성을 변화시키는 데 기여한다. 주사 투과 전자 현미경(STEM)과 밀도 범함수(DFT) 계산을 통해 실리콘 도핑이 강유전상 내부의 단사정 구조 요소를 도입하여 강유전 상태로의 전환을 용이하게 함을 확인했다. 또한 본 연구는 산소 결핍이 실리콘 도핑된 HfO2 필름의 강유전 스위칭 특성에 미치는 영향을 분석한다. 고온 열처리 과정을 통해 조절된 산소 결핍은 분극 반전의 에너지 장벽을 낮추는 것으로 나타났으며, 이는 STEM, 전자 에너지 손실 분광법(EELS), 및 제일원리 계산으로 입증되었다. 이 연구는 또한 이트륨 도핑된 HfO2 (Y:HfO2) 필름에서 -방향 결정 립이 혼합형 고대칭 상(R3m, Pnm21)을 유도하며, 이는 입면 압축 변형 하에서 분극이 강화됨을 밝혀냈다. 나노 수준의 강유전 상 결정립의 상호작용이 Y:HfO2 필름의 전체적인 강유전성을 결정하는 중요한 요소로 나타났다. 강유전 영역 네트워크와 산소 위치 매핑에 대한 정밀 분석은 수직 영역 도메인 벽에서는 분극이 억제되나, 너비가 없는 도메인 벽을 가진 수평으로 정렬된 영역에서는 활성 분극이 관찰됨을 밝혔다. 결론적으로, 이 논문은 강유전 HfO2 박막의 복잡한 특성에 대한 깊은 통찰력을 제공하며, 이를 통해 고급 반도체 기술에서 이 재료들의 미래 설계 및 응용에 대한 중요한 가이드라인을 제시한다.Chapter 1 Introduction . 1 1.1. Ferroelectric HfO2-based thin film 1 1.2. Purpose of research . 2 Chapter 2 Facile Ferroelectric Phase Transition Driven by Si Doping in HfO2 4 2.1. Introduction . 4 2.2. Methods . 6 2.2.1. Sample preparation . 6 2.2.2. STEM measurements . 6 2.2.3. Calculation method . 6 2.2.4. Phonon mode displacement 7 2.3. Results and Discussion 9 2.3.1. Phase stability in HfO2: impact of doping 9 2.3.2. Phonon mode displacement and doping effects . 10 2.3.3. Local bonding characteristics and structural deformation 11 2.3.4. Experimental confirmation using STEM analysis 13 2.3.5. Activation energy analysis and phase transition implications 15 Chapter 3 Enhanced ferroelectric switching speed of Si-doped HfO2 thin film tailored by oxygen deficiency 34 3.1. Introduction 34 3.2. Methods 38 3.2.1. Sample fabrication 38 3.2.2. Sample characterization . 38 3.2.3. Scanning transmission electron microscopy 39 3.2.4. Grain size estimation 40 3.2.5. Electron energy-loss spectroscopy analyses 40 3.2.6. Details of switching dynamics 41 v 3.2.7. Theoretical calculations . 42 3.2.8. Details of Monte Carlo simulations . 43 3.3. Results and Discussion 45 3.3.1. Oxygen deficiency analysis in HfO2 Films 45 3.3.2. Switching dynamics of HfO2 films 47 3.3.3. Theoretical insights and simulation studies on ferroelectric switching . 49 Chapter 4 Atomic-scale scanning of domain network in the ferroelectric HfO2 thin film 61 4.1. Introduction 61 4.2. Methods 65 4.2.1. Sample fabrication and electrical measurements 65 4.2.2. Release and transfer of films 65 4.2.3. (S)TEM, 4D-STEM, automated STEM and iDPC-STEM measurements . 66 4.2.4. STEM and TEM simulations 67 4.2.5. Atomic resolution displacement and strain analysis 68 4.2.6. Computational methods for induction of HS-phase and polarization at vertical domain walls 68 4.2.7. The interface energies between orthorhombic phase domains 70 4.3. Results and Discussion 72 4.3.1. Free-standing ferroelectric Y:HfO2 thin films 72 4.3.2. Inducement of strained polar phase at grain boundaries 74 4.3.3. Phase transformation according to thickness 80 4.3.4. Direct observation of ferroelectric domains . 82 Chapter 5 Summary and Conclusions 117 vi박

Change of the thickness from skin surface to masseter muscle after botulinum toxin injection into human masseter muscle

치과대학/석사Botulinum toxin is widely used to treat masseter muscle hypertrophy. It affects the end of neuron to decrease acetylcholine secretion, causing muscle atrophy which leads to cure. Change of muscle thickness has been reported in many studies. However, there has been no report about change in the thickness from skin surface to masseter muscle. In this study, we aim to measure not only change of muscle thickness but also the change of thickness from skin surface to masseter muscle by using ultrasonography. A total of 17 volunteers were enrolled in this study. 10 patients were assigned to an experimental group (injected 25 U of botulinum toxin on both masseter muscle) and 7 to a control group (injected normal saline). Thickness was measured before injection and 4 weeks, 8 weeks, 12 weeks after the injection each at rest and during maximum clenching. Result showed that thickness from skin surface to masseter muscle did not show significant difference by time at rest (p = 0.063) and maximum contraction state (p = 0.392). There was also no significant difference between experimental group and control group at rest (p = 0.392) and during maximum clenching (p = 0.259). Muscle thickness of experimental group showed a significant difference by time. In conclusion, botulinum toxin injection only affects change in muscle thickness and does not affect thickness from skin surface to masseter muscle.ope

Laryngeal Stridor in a Patient with Multiple System Atrophy

Sleep-related breathing disorders have been extensively reported as a frequent and major problem in patients with multiple system atrophy (MSA). Laryngeal stridor and obstructive sleep apnea are the most common sleep disordered breathing in MSA. We report laryngeal stridor in a patient with multiple system atrophy. A 56-year-old man presented with abnormal breathing sound different from snoring during sleep noticed by his bed partner. He is unaware of his nocturnal stridor. Polysomnography showed obstructive sleep apnea and laryngeal stridor. Laryngoscopy during wakefulness detects normal movement of vocal cord. CPAP (continuous positive airway pressure) eliminated laryngeal stridor and obstructive sleep apnea with pressures of 9 cmH2O.OAIID:oai:osos.snu.ac.kr:snu2007-01/102/2014017262/8SEQ:8PERF_CD:SNU2007-01EVAL_ITEM_CD:102USER_ID:2014017262ADJUST_YN:NEMP_ID:A079623DEPT_CD:801CITE_RATE:0DEPT_NM:의학과SCOPUS_YN:NCONFIRM:

Video Streaming Leveraging Peer-to-Peer Techniques

Video streaming services are getting more popular as the average link capacity in the Internet becomes greater for end hosts. One popular way to disseminate video files among numerous users is to leverage peer-to-peer (P2P) systems. P2P systems can be easily deployed since a participating peers resources (i.e., upload link bandwidth) can be exploited to distribute contents. However, how to adapt to leaving peers and how to encourage peers to contribute resources voluntarily are still challenging issues. In this dissertation, we propose P2P architectures for video on demand and live streaming services. Video on demand services have been increasingly proliferated in the Internet. However, BitTorrent is not designed with video streaming requirements and hence suffers from long setup delay. Therefore, we propose Waterfall that splits the whole swarm into multiple swarms, which are then cascaded by the unit scene sequence. In this way, peers in a swarm download the chunks of the same video unit scene from the peers in the same swarm as well as the ones in the preceding swarm that already moved on to the next unit scene. The average setup delay and maximum playback rate of Waterfall are analyzed. Experiments from a wide area network testbed reveal that Waterfall achieves two to three times higher playback rate and a significantly low setup delay than the prior BitTorrent-based streaming solutions. There also have been a lot of research efforts on peer-to-peer (P2P) live streaming services. In this dissertation, we propose Climber, an adaptive P2P live streaming system with incentives for resilience. Climber is based on the hybrid structure of a tree and a mesh, so as to achieve self-improvement and adaptation to users dynamic joining and leaving. Moreover, Climber substantiates an incentive mechanism that provides better resilience for peers with more upload bandwidth allocated. Simulation results reveal that Climber significantly reduces the topology maintenance cost compared to SplitStream and NICE-PRM. Also, simulation and analytical results verify that Climber can bound the level of disruption by dynamically adapting to the user churning rate. In order to provide a high quality P2P live streaming service, it is essential to handle user dynamics effectively to mitigate streaming disruptions caused by user churn. We collect massive user traces from the largest P2P live streaming site in Korea, namely, Afreeca. Based on the trace results obtained, we analyze user dynamics in the service. In particular, we analyze the user behaviours in terms of three criteria: long-stay users, short-stay users, and user churn. (1) The results show that a certain amount of long-stay users exist in a live streaming session, and it is challenging to recognize the long-stay users online, which will help to provide more resilient live streaming service. (2) Around 20% of the users stay in a session shorter than 1% of the session length. Short-stay users incur high control overhead and we discuss how to efficiently handle the short-stay users. (3) By intentionally disrupting a video streaming, we closely observe the users leaving behaviour and suggest the acceptable recovery time to keep the users remaining the session. We believe our findings can be useful not only to P2P live streaming systems, but also to every live streaming systems.Docto

Catalytic conversion of alginic acid to furfural using 12-tungstophosphoric acid catalyst in tetrahydrofuran/water co-solvent

학위논문 (석사)-- 서울대학교 대학원 : 화학생물공학부, 2016. 2. 김도희.Furfural is one of platform chemicals from biomass conversion processes listed by the US Department of Energy (DOE). The world wide demand for furfural is expected to steadily increase, because furfural can be used as a starting compound in production of furan-derivates such as a polymer unit, organic solvent and various liquid fuel additives. Until now, furfural has been exclusively obtained from hemicelluloses despite increasing demand for furfural, suggesting that diversification of feedstock is necessary for stable supply of furfural. In view of this, we attempted to produce furfural using alginic acid derived from brown seaweeds, and considered a possibility whether alginic acid could be used as an alternative feedstock for furfural production. Alginic acid, main constituent of brown seaweed, is a bio-polymer comprised of hexuronic acid monomers (mannuronic acid and guluronic acid) via β-1,4-glycosidic bond. Notably, the direct conversion of alginic acid to furfural is a somewhat different approach for utilization of the marine algae biomass. In the present work, the decomposition of alginic acid was performed in tetrahydrofuran (THF)/water co-solvent over Brønsted acid catalysts, such as H2SO4, Amberlyst15 and 12-tunstophosphoric acid (H3PW12O40) in order to investigate the effect of the different acid catalysts on the furfural production. Among the catalysts, H3PW12O40 exhibited a higher catalytic performance than other acid catalysts by suppressing the formation of by-product such as an insoluble black precipitate (humin). The maximum furfural yield from alginic acid was 33.8% under the reaction conditions of 180 oC for 30 min in THF/water co-solvent containing 5% (v/v) water over H3PW12O40. To our knowledge, this is the highest furfural yield among the studies about the alginic acid decomposition. In this reaction, THF was a more effective reaction medium than water for furfural production. In particular, addition of small amounts of water to THF drastically enhanced the furfural yield. Furthermore, products distribution with time-stream was investigated to elucidate the reaction pathway. This result showed that alginic acid was initially hydrolyzed to hexronic acid, and then it converted to furfural by removing carbon dioxide and water molecules from the hexuronic acid in presence of acid catalyst. In the reaction pathway, subsequent reaction comprised of decarboxylation and dehydration occurred slower than hydrolysis, which led us to determine rate-limiting steps in the proposed reaction pathway.Abstract 1 List of Tables 6 List of Schemes 7 List of Figures 8 Chapter 1. Introduction 10 1.1. Background 10 1.2. Objective 13 Chapter 2.Experimental 16 2.1. Materials 16 2.2. Catalytic reaction of alginic acid 16 2.3. Analytical methods 17 2.3.1. Gas chromatography (GC) 17 2.3.2. Liquid chromatography-mass spectroscopy (LC-MS) 17 2.3.3. High performance liquid chromatography (HPLC) 18 Chapter 3. Result and discussion 20 3.1. Acid catalyzed reaction of alginic acid to furfural 20 3.2. Thermal effect on furfural production 27 3.3. Water effect on furfural production 32 3.4. Reaction pathway of alginic acid to furfural 36 Chapter 4. Conclusion 45 References 46 요약 (국문초록) 53Maste

뇌암 줄기 세포의 자기 재생과 암 증식에 대한 색소 상피 유래 인자(PEDF)의 역할

학위논문 (박사)-- 서울대학교 대학원 : 협동과정 종양생물학전공, 2015. 2. 정준호.Glioma stem cells (GSCs) require a niche that provides soluble factors to promote GSCs maintenance and self-renewal ability. However, the mechanisms maintaining the stemness of GSCs out of niche microenvironment was not elucidated yet. Here, I identified that an autocrine pigment epithelium-derived factor (PEDF) signaling plays an essential role in regulating self-renewal capability in GSCs out of niche environment. PEDF sustains self-renewal activity of GSCs by Notch1 cleavage, and cleaved Notch1 (NICD) induced expression of Sox2 through the direct interaction with its promoter region. EGFRvIII has been associated with glioma stemness, but the direct molecular mechanism is largely unknown. Here, I showed that EGFRvIII induces the expression and secretion of PEDF via activation of STAT3, thereby promoting self-renewal in GSCs. Silencing of PEDF expression in GSCs reduced self-renewal, tumorigenic potential in orthotopic implantation of GSCs. Furthermore, loss of PEDF expression increased survival period of GSCs-bearing mice. Importantly, the fact that PEDF expression correlated with poor prognosis of glioblasoma patients implicates PEDF as a new therapeutic target for the treatment of GSCs.Abstract i Contents iii List of Figures v List of Tables vii Introduction 1 Material and Methods 4 Results 9 Discussion 49 References 54 Abstract in Korean 64Docto

사람 무릎관절 골관절염 윤활막에서 세포자멸사와 p53에 관한 면역전자현미경적 연구

학위논문(석사)--서울대학교 대학원 :의학과 해부학전공,2001.Maste

Spatial Variation of Early Riparian Vegetation Recovery after the 2020 Summer Extreme Flood along the Seomjingang River, South Korea

학위논문(석사) -- 서울대학교대학원 : 사회과학대학 지리학과, 2024. 2. 김대현.There is growing concern that climate change and flooding has a close relations. In the summer of 2020, a 1-in-500-year rainfall led to a record-breaking extreme flood along the Seomjingang River of southern Korea, which in turn devastated a substantial portion of riparian vegetation. There are ongoing recovery processes on the vegetation along the river. Flooding has a great ecological impact that can directly affect the reciprocal interactions among landform, water flow, and vegetation in riparian ecosystems. In particular, riparian vegetation can significantly contribute to forming overall fluvial landscape dynamics. Therefore, It is essential to understand the ecological processes related to riparian vegetation. The main purpose of this study is to clarify the recovery process of riparian vegetation after an extreme flood throughout a whole river and to identify the very factors that can significantly affect the early recovery of riparian vegetation. I first acquired a total of 5 satellite images(Sentinel-2) collected in May 2020, October 2020, May 2021, 2022, and 2023. Using the bands of the satellite images, I could build a machine-learning model that can classify the riparian vegetation into herbs and woody plants. A lot of analyses were performed using the information on classified vegetation. First, the analysis of variance and annual changes in Theils T suggested the distinct recovery pattern between herbs and woody plants. Second, the choropleth map of the recovery rate visualized the spatial pattern and Morans I index showed the positive spatial autocorrelation of the recovery processes along the whole river. Lastly, I could identify the significant variables that can affect the early recovery processes through the spatial regression models. Based on the above results, I could identify the early recovery pattern of riparian vegetation and the factors that can affect the vegetation recovery. Two general findings in this study are of interest. The first is that the recovery of herbs and woody plants needs to be understood in different contexts. The recovery of herbs and woody plants showed distinct patterns and different factors were related to each recovery. The second is that the global approach along the entire river can be crucial when identifying the processes in fluvial ecosystems. The recovery rate after flood appeared spatially different along the whole river, which implies the importance of understanding the ongoing ecological processes across a broad spatial scale. By examining the recovery pattern of riparian vegetation after an extreme flood throughout a whole river, this study can help to establish spatial priority for the management of the riparian ecosystem after an extreme flood. The management and conservation of riparian ecosystems should take into account both the type of riparian vegetation and the spatial heterogeneity in vegetation recovery processes.집중 호우는 기후 변화와 긴밀한 관계가 있는 것으로 예측되고 있으며, 많은 연구에서 집중 호우로 인한 홍수의 빈도와 강도 증가를 예상하고 있다. 지난 2020년 여름, 한반도 전역에 걸쳐 집중 호우와 대규모 홍수가 발생하였고, 전국에서 많은 피해가 보고되었다. 특히, 섬진강 유역에는 500년 재현 주기로 발생한 집중 호우가 대홍수로 이어져 하천생태계에 큰 교란이 발생하였다. 홍수로 인해 많은 수변 식생이 파괴되었으며, 그 이후 회복의 과정을 거치고 있다. 이에 본 연구는 대규모 홍수 발생 이후 초기 수변 식생 회복 프로세스를 다양한 측면에서 확인하는 것을 연구 목적으로 하였다. 홍수 이후의 회복을 파악하기 전에 홍수로 인한 지형 변화와 식생 피해를 먼저 파악하였고, 수변 식생 회복 프로세스는 진행 양상, 공간적 변이, 회복에 영향을 미치는 주요한 요인 세 가지 측면에서 다양한 분석을 통해 확인하였다. 분석에 앞서 초목 분류 모델을 구축하여 가장 높은 정확도를 보이는 모델을 선정하고, 하천 생태계 전역에 분포하는 식생을 초본과 목본으로 분류하여 파악하였다. 다음으로, Theil 지수와 분산 분석 및 사후검정을 통한 회복 프로세스의 진행 양상을 확인하였다. 또한, 단계구분도를 통한 시각화 및 공간적 자기상관 계산을 바탕으로 회복 프로세스의 공간적 변이를 살폈다. 마지막으로 초본 회복률과 목본 회복률 각각을 종속 변수로 한 다중 및 공간 회귀 분석을 통해 초기 식생 회복률에 영향을 미치는 주요한 요인을 파악하였다. 먼저, 초본과 목본의 회복양상에서 나타나는 차이를 분산 분석 결과와 Theil 지수 변화를 통해 확인하였다. 초본의 경우 3년이라는 짧은 시간에서도 전역에 걸친 회복을 파악할 수 있었다. 반면에 목본의 회복은 일부 하도 구간에서 국지적으로 일어나고 있었다. 다음으로, 단계 구분도를 통한 시각화와 모란 지수를 통해 목본의 회복 프로세스가 초본에 비해 공간적으로 더 군집하는 경향이 있다는 것을 확인하였다. 마지막으로, 공간 회귀 모델을 통해 초본과 목본의 회복 프로세스 각각에 영향을 미치는 주요한 요인을 확인하였다. 초본 회복률은 초본 피해율, 홍수 전 식생 구성비, 홍수 직후 초본 및 목본 피도, 퇴적 면적과 양의 관계를 보이는 것으로 나타났다. 한편, 목본의 회복률은 홍수 전 식생 구성비와 음의 관계에 있으며, 홍수 직후 목본의 피도와는 양의 관계에 있는 것으로 나타났다. 초본과 목본의 회복 프로세스에 영향을 미치는 주요한 요인은 차이가 나며, 특히 식생의 구성비와 홍수 직후 식생 분포는 초본과 목본 회복에 중요하게 작용한다. 본 연구에서 파악한 대규모 홍수 이후 하천 생태계에서 나타나는 초기 식생 회복 프로세스와 관련해서는 크게 두 가지 논의가 가능하다. 먼저, 초본과 목본의 회복은 서로 다른 맥락에서 파악될 필요가 있다는 것이다. 본 연구에서는 Theil 지수를 비롯하여, 분산 분석, 주성분 분석, 단계구분도를 통한 시각화, 공간 회귀 분석까지 다양한 통계 방법을 적용하여 초본과 목본의 회복이 다른 양상을 보이며, 각 회복에 영향을 미치는 주요한 요인이 다르다는 사실을 확인할 수 있었다. 홍수에 대한 식생의 반응을 파악할 때 초목에 대한 분류가 선행될 필요가 있다. 다음은 하천생태계에 나타나는 프로세스를 연구할 때는 전역적 접근이 중요하다는 것이다. 본 연구에서는 섬진강 전역에서 나타나는 초기 식생 회복을 확인하였고, 이를 통해 초기 식생 회복이 공간적으로 이질적으로 나타난다는 것을 확인할 수 있었다. 최근 변하고 있는 교란의 양상을 고려한다면 넓은 공간 범위에 걸친 생태계의 반응을 파악할 필요가 있다. 대규모 홍수에 대한 생태계의 반응을 전역적으로 살피는 연구는 다양한 분야에서 기초 정보로 활용할 수 있으며, 이를 바탕으로 더 효과적인 생태계 관리에 기여할 수 있을 것이다.제 1 장 서론 1 제 1 절 연구배경 1 제 2 절 선행연구 검토 및 평가 2 1. 홍수 이후 하천생태계 변화 연구와 전역적 접근의 필요성 2 2. 식생 회복 연구의 시공간적 스케일과 초기 식생 회복의 공간적 변이 파악의 필요성 2 3. 식생 지수를 활용한 식생 회복 연구와 식생 구분의 필요성 3 4. 홍수 이후의 수변 식생 회복 연구와 대규모 홍수 이후 식생 회복 연구의 특수성 3 제 2 장 연구 목적 및 연구의 이론적 배경 6 제 1 절 연구 목적 6 제 2 절 연구의 이론적 배경 9 1. 하천 생태계에서 나타나는 상호작용과 수변 식생의 역할 9 2. 홍수의 발생과 하천 생태계에서 나타나는 상호작용 10 3. 초기 식생 회복 파악의 중요성 12 제 3 절 용어의 정의 14 1. 수변 공간과 수변 식생 14 2. 식생 피해와 식생 회복 15 제 3 장 연구 지역 및 방법 17 제 1 절 연구 지역 17 1. 연구 지역 개관 17 2. 연구 지역의 지형·지질 21 3. 연구 지역의 기후·기상 21 4. 연구 지역의 식생 22 제 2 절 연구 방법 23 1. 현장 조사 23 2. 초목 분류 방법 24 3. 홍수로 인한 침식 및 퇴적 면적 계산 방법 28 4. 식생 피해율과 회복률 계산 방법 29 5. 통계 방법론 31 제 4 장 연구 결과 36 제 1 절 초목 분류 모델 36 제 2 절 대홍수로 인한 지형 변화 38 1. 대홍수로 인한 퇴적 38 2. 대홍수로 인한 침식 39 3. 대홍수로 인한 지표 변화 면적 40 제 3 절 대홍수로 인한 식생 피해 43 1. 대홍수로 인한 피도 변화 43 2. 대홍수로 인한 초본 피해 45 3. 대홍수로 인한 목본 피해 46 제 4 절 대홍수 이후 식생 회복의 진행 양상 48 1. 초본 회복 프로세스의 진행 48 2. 목본 회복 프로세스의 진행 49 3. 단위 면적 당 피도와 식생 회복률의 불평등 지수 변화 50 제 5 절 대홍수 이후 식생 회복의 공간적 변이 53 1. 초본 회복률의 공간적 변이 53 2. 목본 회복률의 공간적 변이 54 제 6 절 대홍수 이후 식생 회복에 영향을 미치는 주요 요인 55 1. 식생 회복률과 독립 변수의 상관관계 분석 57 2. 식생 회복률에 대한 회귀 분석 결과 57 제 5 장 토의 60 제 1 절 초목 구분의 필요성 60 제 2 절 대홍수로 인한 지형 변화 61 제 3 절 대홍수로 인한 수변 식생의 피해 62 제 4 절 수변 식생 회복의 진행 양상 63 제 5 절 수변 식생 회복의 공간적 변이 65 제 6 절 수변 식생 회복에 영향을 미치는 주요 요인 66 제 7 절 정리 68 제 6 장 결론 70 제 1 절 요약 70 제 2 절 결론 72 참고문헌 74 Abstract 87석

Effective concolic search strategy using dynamic taint analysis

학위논문(석사) - 한국과학기술원 : 전산학부, 2020.2,[iv, 38 p. :]Concolic 테스팅은 대상 프로그램의 모든 경로를 탐색하는 것을 목표로 테스트 케이스를 생성하는 소프트웨어 자동화 테스팅 기법이다. 하지만 프로그램의 모든 경로를 탐색하는 것은 많은 비용이 들기 때문에, 분기 커버리지를 높이 달성할 수 있는 가장 유망한 경로부터 먼저 살펴보는 것이 중요하다. 어떤 경로부터 탐색할지 결정하는 전략을 Concolic 탐색 전략이라고 부른다. 기존의 Concolic 탐색 전략들(DFS, rev-DFS, CFG, random)은 대상 프로그램에 있는 함수들 간의 데이터 의존도를 고려하지 않고 방문할 분기를 결정하기 때문에 분기 커버리지가 낮게 나오는 경우가 있다. 본 연구는 동적 테인트 분석을 통해 함수 간 데이터 의존도를 함수 간 데이터 흐름을 기반으로 정의하고 함수 간 데이터 의존도를 바탕으로 새로운 concolic 탐색 전략 Taint를 설계하였다. Taint는 타겟 함수 g의 커버하지 못한 분기를 커버하고자 할 때, 함수 f에 대한 함수 g의 데이터 의존도가 높은 경우(즉, 함수 f에서 함수 g로 변수의 값들을 많이 보내고), 함수 f의 분기를 부정하거나 함수 g의 분기를 부정해서 함수 g에서 커버하지 못한 분기를 커버하도록 하는 휴리스틱이다. 이러한 접근 방식은 함수 f가 함수 g로 보낸 변수의 값들이 함수 g의 실행 경로를 결정한다는 직관에서 비롯된다. 또한, 함수 간 데이터 의존도를 계산할 때, 고려해야 할 여러 가지 요소들 중에서 3가지 요소들을 고려하였다. 동적 테인트 분석은 함수 간 데이터 의존도의 측정에 기반이 되는 함수 간 데이터 흐름을 추출하기 위해 사용되었다. Taint는 기존의 Concolic 탐색 전략들을 사용했을 때보다 1.2%p~7.1%p 더 높은 분기 커버리지를 달성할 수 있다.한국과학기술원 :전산학부

공기 차압을 이용한 공기열원 열펌프의 제상시기 탐지방법에 대한 연구

학위논문 (석사)-- 서울대학교 대학원 : 공과대학 기계항공공학부(멀티스케일 기계설계전공), 2018. 8. 김민수.This study shows the feasibility and effectiveness of the detection method for determining the defrosting start time by measuring the air static pressure differences between the atmospheric pressure and the pressure measured before the outdoor unit fan in air source heat pump system (ASHP). Generally, the frosting occurs under cold and humid environmental air condition, which means outdoor air temperature around the heat exchanger is lower than both dew point temperature of air and freezing temperature of water. As the frost accumulation increases, the air pressure differences occur between the atmospheric pressure and the pressure measured inside the outdoor unit because of becoming narrow the area of airflows. It is possible to predict the frost accumulation of the heat pump evaporator indirectly measuring these changes of the pressure differences. The pressure of the air is consist of the static pressure and dynamic pressure. The static pressure is used for obtaining the consistent and reliable data for the airflows. If the dynamic pressure is used, the experimental data will be influenced by the position of the differential pressure sensors and be possible of being blocked by the dust or moisture. On the contrary, if we use the static pressure, the negative pressure occurs at the position of measuring the pressure inside the outdoor unit. When the outdoor fan operates, the pressure inside the outdoor unit becomes lower than the external pressure and the negative pressure is generated. This shows that the possibility of going the dust or moisture inside sensors is minimized and the static pressure is less influenced by the change of the air velocity, unlike the dynamic pressure. The pressure measurement position inside the outdoor unit is an important factor in this study. The heat exchanger is generally divided into three parts such as high, middle and low. As the pressure is measured at a position close to the fan, the value of the static pressure increases. On the contrary, it gets the lower static pressure value being farther away from the fan. As the frost accumulation increases, the air pressure differences between the atmospheric pressure and the pressure inside the outdoor unit also increases. It shows that the position of measuring the pressure is getting lower, the pressure differences become bigger. Measuring the pressure at the same height, the distance between the measuring point and the heat exchanger is an important factor to consider. The pressure is measured at five locations: center, front, rear, right, and left to find the optimal position at the same height. The distance between each sensor is 8 cm and the right position is about 3 cm away from the outdoor heat exchanger. The differential pressure value increases as the pressure measurement position is closer to the heat exchanger due to the influence of the airflows. The performance of various operating conditions such as pressure measurement position, outdoor air temperature, relative humidity and compressor speed is tested to identify the relation of pressure drop with the heating capacity of the system. The pressure difference control method is suggested by providing an appropriate threshold value and comparing with the result with other estimation methods. As a result, the suggested method is more reliable than conventional time control method for deciding the defrosting start time. Conclusively, the defrosting start time can be controlled by measuring the air static pressure difference between the atmospheric pressure and the pressure measured before the outdoor unit fan in the air source heat pump system.Contents Abstract i Contents v List of Tables viii List of Figures ix Nomenclatures xi Chapter 1. Introduction 1 1.1 Background of the study 1 1.2 Literature survey 7 1.2.1 Various methods to determine the defrosting start time 8 1.2.2 Application of the differential pressure 11 1.3 Objectives and scopes 12 Chapter 2. Experimental setup and procedures 14 2.1 Introduction 14 2.2 Experimental procedures and conditions 21 2.3 Data reduction and uncertainty analysis 22 2.4 Static pressure 25 2.5 Position of measuring the pressure 25 Chapter 3. CFD analysis of the pressure distribution inside of the outdoor unit 27 3.1 Introduction 27 3.2 Description of CFD Model and boundary conditions 28 3.3 CFD analysis result 31 3.3.1 Pressure distribution in no frosting condition 31 3.3.2 Pressure distribution in frosting condition 33 3.4 Summary 36 Chapter 4. Experimental results by measuring differential pressure 37 4.1 Introduction 37 4.2 Optimal position of sensing the static pressure 39 4.2.1 Optimal position at the same height 39 4.2.2 Optimal position at the different height 45 4.3 Pressure differences under various conditions 47 4.3.1 Various dry-bulb temperature conditions 47 4.3.2 Various relative humidity conditions 50 4.3.3 Various compressor speed conditions 52 4.3.4 Various fan speed conditions 54 4.4 Summary 56 Chapter 5. Conclusion 59 References 60 Abstract (Korean) 63Maste